Image transfer mechanism



July 14, 1970 o. GNAGE 3,520,603

IMAGE TRANSFER MECHANISM Filed July 1, 1968 OLIVER W. GNAGE /4ZZ IAgIIVt EKN 'I'OR. BY w Mu f ATTORNEYS United States Patent 3,520,603 IMAGE TRANSFER MECHANISM Oliver W. Gnage, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed July 1, 15168, Ser. No. 741,386 Int. Cl. G03g /00 US. Cl. 355-4 7 Claims ABSTRACT OF THE DISCLOSURE A transfer roller with a receiver sheet attached is moved across each of a plurality of photoconductive chips carrying an electrostatic toner image which is transferred sequentially to the receiver. The transfer roller is normally driven by a drive gear through a pitch ring and rack. However, the transfer roller is rotatable relative to the drive gear from an initial rotationally aligned position so that the rotational speed of the receiver and hence the transfer roller is controlled by the frictional rolling engagement between the photoconductive chips and the receiver. The radius of the drive gear is larger than the sum of the radius of the transfer roller and the thickness of the receiver. Thus during engagement between the photoconductive chips and the receiver, the transfer roller and the receiver are driven at a greater rotational speed than the transfer roller drive gear so that no relative motion exists between the chips and receiver along the line of transfer to avoid smearing. After transfer of the image from each chip, the roller is snapped back to its initial aligned position relative to the drive gear by a spring connected between the two for the next transfer.

CROSS-REFERENCE TO RELATED APPLICATION An apparatus of this invention may be utilized in the device disclosed in commonly assigned US. patent application, Ser. No. 741,359, filed July 1, 1968, entitled Printing Apparatus to John S. Pollock.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a transfer device for the transfer of electrostatic toner images from the surface of a photoconductive component to a receiving surface and more particularly to such a device for transferring images from a plurality of photoconductive components onto a single receiving surface in registry and without smearing.

Description of the prior art The problem of registering electrostatic toner images has been largely ignored because in most instances only one image was transferred to each receiver. Most attempts to superimpose a plurality of toner images involve trying to precisely align optical systems for three color separation images with the exposure stations and separate transfer stations to provide exact alignment of electrostatic toner images on a receiver to obtain registry. However, as a practical matter, these methods are not very satisfactory because of extreme difiiculty in maintaining all parts in proper alignment at all times. Thus, the need for a convenient way of aligning each photoconductor with the receiver for each transfer of an image is apparent. In addition unless there is no relative motion between the receiver and the photoconductor along the line of transfer, smearing of the toner image during transfer may occur.

This alignment problem is of particular importance in copying color originals. In the usual electrophotographic process, an original, such as a color negative, is broken down into three color components by the use of beam splitters filters, etc. as is Well known in the art. Colorseparatlon images thus formed are then projected onto different photoconductive surfaces to form three separate electrostatic images. These images are each toned w1th a toner having a color complementary to each color separation image. The toned images are finally transferred in registry to a receiver to form a composite color print. Unless the registration of the toner images is held within very narrow limits, the resulting print will be unsatisfactory.

SUMMARY OF THE INVENTION The transfer mechanism of this invention includes a transfer roller which is turned by drive means, such as a gear and rack, until the receiver wrapped around the roller comes in contact with a photoconductive chip carrying an electrostatic toner image. The gear pitch radius is slightly larger than the sum of the radius of the transfer roller and the thickness of the receiver. Hence, the roller rolls across the chip at a higher r.p.m. than the gear because the roller is now driven by the frictional force between the receiver and chip. This causes relative motion between the gear and the roller so that they are no longer rotationally aligned, stretching a resilient means interconnecting them. When the roller reaches the end of the first chip, it is aligned with the gear by the resilient means and is driven by the gear to the next chip. Thus, no slipping will occur between the receiver and the photoconductor due to any mismatch of the di ameter of the roller and the forward velocity thereof and smearing of the image is substantially avoided. Conveniently, the pitch circumference of the gear is exactly equal to the distance between corresponding points on adjacent chips so that the receiver is in exactly the same position at the beginning of each transfer. Of course, the gear is driven so that it makes exactly a precise number of revolutions between chips.

Additional novel features of this invention will become apparent from the description which follows, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary side elevation of the transfer mechanism of this invention prior to engagement with a photoconductive chip;

FIG. 2 is a fragmentary, enlarged top plan view showing details of the gear and pitch ring for the transfer mechanism of FIG. 1, but with the transfer roller rotatably displaced from the gear; and

FIG. 3 is an enlarged fragmentary side elevation of a portion of the transfer mechanism of FIG. 1 showing the mechanism in engagement with a photoconductive chip wherein the transfer roller is rotatably displaced from the gear.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with this invention, a transfer mechanism is provided which can be utilized in a system wherein separate photoconductive surfaces 10 on photoconductive chips 11 are exposed to different light images to form corresponding latent electrostatic images thereon. These images are then developed by any suitable means and moved to the transfer mechanism where they are held in transfer position against registration pins 12, as by electromagnets (not shown). The registration pins are spaced so that corresponding portions of the separate images are transferred in registry to a receiver 13, wrapped around and supported by a transfer roller 14, as shown in FIG. 1. Transfer roller 14 is rotatably mounted on a shaft 14a in a frame 15 attached to a timing belt 16 which drives a transfer roller across the photoconductive chips by means of motor 17 connected to the timing belt 16 through endless belt 18. At either or both ends of transfer roller 14, drive means, such as drive gear 19 is axially mounted on shaft 14a and rotatable with respect to the transfer roller, engages idler gear 21. Thus shaft 14a serves as a coupling means between transfer roller 14 and drive gear 19. Idler gear 21 in turn engages rack 22 so that upon movement of the transfer roller by the timing belt 16 the roller will be rotatably driven as indicated by the arrows. Drive gear 19 has a circumference equal to the distance between corresponding portion of adjacent chips. Drive gear 19 is sized so that it will make exactly one revolution between chips or some multiple number of revolutions between chips, so that corresponding portions of the toner image on each chip will be transferred to a receiver in registry. The center distance between idler gear 21 and rack 22 may be controlled by pitch ring 23 riding on rail 24 which runs parallel to rack 22. Conveniently, pitch ring 23 has a diameter which is the same as the gear pitch diameter of idler gear 21 and rail 24 is at the same height as the pitch line of rack 22.

Unless the diameter of the roller, including the thick ness of receiver 13 is eactly matched to the forward velocity of the roller, some slipping will occur between the receiver and the photoconductor 11 causing a smearing of the electrostatic toner image during transfer. To reduce this possibility, a means is provided to permit relative motion between transfer roller 14 and drive gear 19. A stop 25 on transfer roller 14 is normally held in engagement with a pin 26 on drive gear 19 by means of a spring 27, as shown in FIGS. 1 and 2 so that the gear and transfer roller rotate together in aligned relationship. Advantageously, roller 14 is slightly smaller than the pitch gear diameter of drive gear 19. Thus, when the roller rolls across a photoconductive chip under friction at a higher r.p.m. than the gear, there is relative rotational motion between gear 19 and roller 14 causing spring 27 to be stretched as in FIG. 3. When the roller reaches the end of a chip, it will be aligned with gear 19 by spring 27. By proper sizing of drive gear 19, the transfer roller will rotate exactly one revolution, or some multiple number of revolutions, so that it is properly positioned for the beginning of the next transfer. Thus, corresponding portions of the image on each of the chips will be transferred in substantial registration with each other and without smearing onto the receiver.

From the foregoing, the novel features of this invention and the advantages thereof are readily apparent. A transfer roller, which is adapted to support a receiver, has been provided which is caused to rotate by engagement with a chip at a higher r.p.m. than its drive gear without making the diameter of the transfer roller correspond exactly to the forward velocity of the roller. A spring permits this relative movement during the transfer operation and then re-registers the roller with the drive mechanism after transfer so that the roller is properly positioned for a subsequent transfer. Thus, no relative motion exists between the receiver and the chip along the line of contact therebetween and smearing of the image is substantially eliminated.

The invention has been described in considerable detail with reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. In a transfer mechanism for transferring, in registry, an electrostatic toner image from each of a plurality of photoconductive chips onto a single receiver, said mechanism including means positioning said photoconductive chips; a rotatable transfer roller for supporting a receiver during transfer; a drive means coupled to said transfer roller in rotational alignment therewith for rotating said transfer roller and means for moving said transfer roller 4 past said photoconductive chips, the improvement comprising:

coupling means interconnecting said drive means and said transfer roller so that said roller is rotatable at a higher rotational speed than said drive means upon engagement of said receiver by each of said photoconductive chips so that no relative motion exists between said photoconductive chips and said receiver during transfer of said toner images therebetween; and

resilient means interconnecting said drive means and said transfer roller to realign said transfer roller with said drive means after disengagement with each of said photoconductive chips.

2. In a transfer mechanism, as claimed in claim 1, the

improvement further comprising:

a stop on said roller engageable with said drive means after said receiver has received said toner image, to align said roller with said drive means under the influence of said resilient means.

3. In a transfer mechanism, as claimed in claim 2,

wherein:

said resilient means is connected between said stop and said drive means.

4. In a transfer mechanism, as claimed in claim 2, the

improvement further comprising:

a pin extending from said drive means engageable by said stop for aligning said roller and said drive means.

5. A transfer mechanism for transferring, in registry, an electrostatic toner image from each of a plurality of photoconductive chips onto a single receiver, said mechanism comprising:

means positioning said chips at equally spaced distances along a transfer path;

a rotatable transfer roller for supporting a receiver during image transfer;

drive means for moving said transfer roller across said photoconductive chips;

a drive gear for rotating said transfer roller, said drive gear having a pitch radius larger than the sum of the radius of the transfer roller and the thickness of the receiver, the circumference determined by said pitch radius also being equal to the distance between corresponding portions of adjacent chips;

a shaft interconnecting said drive gear and said transfer roller, said drive gear and transfer roller being rotatably mounted thereon so that said roller is rotatable at a higher rotational speed than said drive means upon engagement of said receiver by each of said photoconductive chips so that no relative motion exists between each of said photoconductive chips and said receiver during transfer of said toner images therebetween;

a rack having a pitch line extending along said transfer path;

a circular idler gear interconnecting said drive gear and said rack; and

resilient means interconnecting said drive gear and said transfer roller to realign said transfer roller with said drive gear after disengagement of said transfer roller from each of said photoconductive chips.

6. A transfer mechanism, as claimed in claim 5, further including:

a rotatable pitch ring axially aligned with and connected to said idler gear, said ring having a diameter the same as the pitch diameter of said idler gear; and

a rail extending along said rack and having a surface along which said pitch ring may roll, said surface being aligned with and parallel to said pitch line of said rack.

7. A transfer mechanism, as claimed in claim 5, further including:

a stop on said transfer roller, said resilient means extending between said stop and said gear; and

a pin on said gear engag eable by said stop to align 3,399,611 9/1968 Lusl r 355-4 said transfer roller with said drive gear after trans- 3,414,353 12/ 1968 Schwardt 355--18 fer each image NORTON ANSHER, Primary Examiner References Cited 5 L. H. MCCORMICK, 111., Assistant Examiner UNITED STATES PATENTS US. Cl. X.R.

3,357,830 12/1967 Bixby 118-637 XR 7- ;1 37 

